Electrophotographic photosensitive drum, process cartridge, and electrophotographic image forming apparatus

ABSTRACT

An electrophotographic photosensitive drum is for a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus. The main assembly includes a motor, and a gear having a non-circular twisted hole. The drum includes a cylinder having a non-circular twisted projection engageable with the hole to receive a driving force from the main assembly when the cartridge is mounted to the main assembly. A recess is formed in of the projection and has a bottom portion and a side surface portion. When the projection receives a pulling force toward the hole by rotation of the gear with the projection and the hole being engaged with each other, the bottom portion contacts a spherical surface portion provided at a central portion of the hole, and the side surface portion contacts the spherical surface portion.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an electrophotographic photosensitivedrum (which hereinafter will be referred to simply as “photosensitivedrum”), a process cartridge employing an electrophotographicphotosensitive drum, and an electrophotographic image forming apparatusemploying such a process cartridge.

Here, an electrophotographic image forming apparatus means an apparatusfor forming an image on a recording medium (for example, paper, OHPsheet, etc.) with the use of an electrophotographic image formingmethod. For example, an electrophotographic copying machine, anelectrophotographic printer (for example, LED printer, laser beamprinter, etc.), a facsimileing machine, a wordprocessor, etc., can beincluded in the category of an electrophotographic image formingapparatus.

A process cartridge means a cartridge which is removably mountable inthe main assembly of an electrophotographic image forming apparatus, andin which a minimum of one among a charging means as a processing means,a developing means as a processing means, and a cleaning means as aprocessing means, and an electrophotographic photosensitive drum, areintegrally placed in order to make them removably mountable in the mainassembly of the image forming apparatus. It also includes a cartridgewhich is removably mountable in the main assembly of anelectrophotographic image forming apparatus, and in which a minimum of adeveloping means as a processing means, and an electrophotographicphotosensitive drum, lo are integrally placed in order to make themremovably mountable in the main assembly of the image forming apparatus.

A process cartridge system has long been employed in the field of anelectrophotographic image forming apparatus.

A process cartridge system makes it possible for a user to maintain anelectrophotographic image forming apparatus by himself, without relyingon a service person, improving substantially operational efficiency.Therefore, it is widely used in the field of an image forming apparatus.

In recent years, demand for an electrophotographic color image formingapparatus capable of forming a color image has been increasing.

An electrophotographic image forming apparatus forms four independentimages different in color. Thus, if any of the four images is deviatedfrom the target (ideal) position on the peripheral surface of thephotosensitive drum, this results in the formation of a color image withcolor deviation.

The countermeasure for preventing the formation of a color image withthe above described color deviation is as follows. The main assembly ofan electrophotographic color image forming apparatus is provided with agear which receives driving force from a motor. This gear is providedwith a spiral hole, which is located in the center thereof to transmitthe driving force to a photosensitive drum. One of the lengthwise endsof the photosensitive drum is provided with a spiral projection, whichfits into the spiral hole on the main assembly side to transmit thedriving force. With the provision of this structural arrangement, thedriving force from the motor on the main assembly side is transmitted tothe photosensitive drum through the wall of the spiral hole on the mainassembly side, and the spiral projection on the photosensitive drumside, precisely rotating the photosensitive drum (Japanese Laid-openPatent Application 2003-5475).

In other words, the above described structural arrangement raises thelevel of accuracy at which the photosensitive drum is rotated.

SUMMARY OF THE INVENTION

The present invention is a further development of the above describedprior art.

The primary object of the present invention is to provide a combinationof a photosensitive drum, a process cartridge, and anelectrophotographic image forming apparatus, which is superior to thatin accordance with the prior art, in terms of the level of accuracy atwhich a photosensitive drum is rotated.

Another object of the present invention is to provide a combination of aphotosensitive drum, a process cartridge, and an electrophotographicimage forming apparatus, which prevents the photosensitive drum fromfluctuating in rotational velocity.

Another object of the present invention is to provide a combination of aphotosensitive drum, a process cartridge, and an electrophotographicimage forming apparatus, which precisely positions the photosensitivedrum relative to the main assembly of the image forming apparatus byplacing the hemispherical portion of the drive shaft on the mainassembly side of the image forming apparatus, in contact with the bottomof the hole of the projection on the photosensitive drum side, in termsof the lengthwise direction of the photosensitive drum, and by placingthe base portion of the hemispherical portion in contact with thelateral surface of the hole, in terms of the direction perpendicular tothe lengthwise direction of the photosensitive drum.

Another object of the present invention is to provide a combination of aphotosensitive drum, a process cartridge, and an electrophotographicimage forming apparatus, which is superior in image quality to that inaccordance with the prior art.

Another object of the present invention is to provide a combination of aphotosensitive drum a process cartridge, and an electrophotographicimage forming apparatus, which prevents the photosensitive drum fromfluctuating in rotational velocity even if the axial line of the drivinggear on the main assembly side of the image forming apparatus becomestilted relative to the axial line of the photosensitive drum.

Another object of the present invention is to provide a combination of aphotosensitive drum, a process cartridge, and an electrophotographicimage forming apparatus, which minimizes the fluctuation of therotational velocity of the photosensitive drum in order to minimize thecolor deviation to form a high quality image.

According to an aspect of the present invention, there is provided anelectrophotographic photosensitive drum for a process cartridgedetachably mountable to a main assembly of an electrophotographic imageforming apparatus for forming an image on a recording material, saidmain assembly including a motor, a main assembly gear for transmitting adriving force from said motor, and a non-circular twisted hole having asection with a plurality of corner portions provided at a centralportion of the main assembly gear, said non-circular twisted hole beingrotatable integrally with the main assembly gear, saidelectrophotographic photosensitive drum comprising (a) a cylinder havinga photosensitive layer on a peripheral surface thereof; (b) anon-circular twisted projection provided on one longitudinal end of saidcylinder and having a section with a plurality of corner portions, saidnon-circular twisted projection being engageable with the hole of themain assembly of the apparatus to receive transmission of a drivingforce from the main assembly of the apparatus when said processcartridge is mounted to the main assembly of the apparatus; a recessformed in a central portion of said projection and having a bottomportion and a side surface portion, wherein when said projectionreceives a pulling force toward said hole by rotation of the mainassembly gear with the projection and the hole being engaged with eachother, said bottom portion is contacted to a spherical surface portionprovided at a central portion of said hole, and said side surfaceportion is contacted to said spherical surface portion; wherein whensaid electrophotographic photosensitive drum is mounted to the mainassembly of said apparatus, and said electrophotographic photosensitivedrum receives a driving force for rotation from the main assembly of theapparatus, an end of said spherical surface portion is contacted to saidbottom portion, and said spherical surface portion is contacted to saidside surface portion.

The present invention can improve a photosensitive drum in the level ofaccuracy at which it is rotated.

The present invention can prevent a photosensitive drum from fluctuatingin rotational velocity.

According to the present invention, the photosensitive drum is preciselypositioned relative to the main assembly of the image forming apparatusby placing the hemispherical portion of the drive shaft on the mainassembly side of the image forming apparatus, in contact with the bottomof the hole of the projection on the photosensitive drum side, in termsof the lengthwise direction of the photosensitive drum, and by placingthe base portion of the hemispherical portion in contact with thelateral surface of the hole, in terms of the direction perpendicular tothe lengthwise direction of the photosensitive drum.

The present invention can improve in image quality anelectrophotographic image forming apparatus.

The present invention can prevent a photosensitive drum from fluctuationin rotational velocity even if the axial line of the gear on the mainassembly side of an image forming apparatus becomes tilted relative tothe axial line of the photosensitive drum.

These and other objects, features, and advantages of the presentinvention will become more apparent upon consideration of the followingdescription of the preferred embodiments of the present invention, takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the color image forming apparatus in oneof the preferred embodiments of the present invention.

FIG. 2 is a sectional view of the process cartridge in the preferredembodiment of the present invention.

FIG. 3 is a perspective view of the process cartridge in the preferredembodiment of the present invention.

FIG. 4 is a schematic perspective view of the main assembly of the imageforming apparatus and process cartridge, showing how the processcartridge is mounted into the apparatus main assembly.

FIG. 5 is a perspective view of the drum flange.

FIG. 6 is a sectional view of the drum driving force transmissionmechanism in the preferred embodiment of the present invention.

FIG. 7 is a sectional view of the drum driving force transmissionmechanism in the preferred embodiment of the present invention.

FIG. 8 is a sectional view of the drum driving force transmissionmechanism in the preferred embodiment of the present invention.

FIG. 9 is a perspective view of the drum driving force transmissionmechanism in the preferred embodiment of the present invention.

FIG. 10 is a graph, which provides the data obtained by measuring therotational velocities of the photosensitive drum in the preferredembodiment and a photosensitive drum in accordance with the prior art,in order to compare the preferred embodiment of the present inventionwith the embodiment of the prior art, in terms of the irregularity inthe rotational velocity of a photosensitive drum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the combination of the electrophotographic photosensitivedrum, process cartridge, and electrophotographic image formingapparatus, in one of the preferred embodiments of the present invention,will be described with reference to the appended drawings.

In the following description of the preferred embodiment of the presentinvention, an image forming apparatus is described as anelectrophotographic full-color image forming apparatus employing fourprocess cartridges removably mountable in the main assembly of the imageforming apparatus. However, this embodiments is not intended to limitthe number of the process cartridges to be removably mounted in an imageforming apparatus; in other words, the number of the process cartridgesto be removably mounted in an image forming apparatus is optional, andmay be determined according to the requirements. For example, in thecase of an image forming apparatus for forming a monochromatic image,the number of the cartridges mounted in the main assembly of theapparatus is one. Also in the following description of the preferredembodiment of the present invention, the image forming apparatus isdescribed as a printer, which is one form of an image forming apparatus.However, this embodiment is not intended to limit the application of thepresent invention to a printer. In other words, the present invention isalso applicable to image forming apparatuses other than a printer, forexample, a copying machine, a facsimileing machine, or a machine(multifunction image forming apparatus) capable of performing one ormore functions of the preceding image forming apparatuses. Moreover, theapplication of the present invention is not limited to an image formingapparatus employing an electrostatic transfer belt. That is, the presentinvention is also applicable to an image forming apparatus which employsan intermediary transferring member, and in which a plurality ofdeveloper images different in color are sequentially transferred inlayers onto the intermediary transferring member, and then, aretransferred all at once onto a recording medium.

Further, the materials and configurations of the structural componentsin the following embodiment of the present invention, and theirpositional relationship, are optional, and are to be changed asnecessary according to the structure of an apparatus to which thepresent invention is applied, and various other factors. In other words,the following embodiment of the present invention is not intended tolimit the scope of the present invention.

[General Structure of Full-color Image Forming Apparatus]

First, referring to FIG. 1, an electrophotographic full-color imageforming apparatus in accordance with the present invention will bedescribed. FIG. 1 is a vertical sectional view of a full-color laserbeam printer, which is one form of an image forming apparatus, showingthe general structure thereof.

As shown in FIG. 1, the image forming apparatus 100 in accordance withthe present invention employs four process cartridges 7, one for each ofthe four color components, that is, yellow (Y), magenta (M), cyan (C),and black (K), and a conveying means for conveying a recording medium tothe four process cartridges 7 and discharges the recording medium out ofthe main assembly of the image forming apparatus. Each of the fourcartridges 7 comprises an electrophotographic photosensitive drum (whichhereinafter will be referred to simply as “photosensitive drum”) 1 whichis rotated at a predetermined peripheral velocity.

Each cartridge 7 comprises a photosensitive drum 1 (1Y, 1M, 1C, and 1K)which is rotationally driven, a charge roller 2(2Y, 2M, 2C, and 2K) foruniformly charging the peripheral surface of the photosensitive drum 1,a development unit 4 (4Y, 4M, 4C, and 4K) having a development roller 40as a developing means for developing an electrostatic latent imageformed on the photosensitive drum 1, by adhering developer to theelectrostatic latent image, a cleaner unit 50 (50Y, 50M, 50C, and 50K)having a cleaning blade 60 as a cleaning means for removing the residualdeveloper, that is, the developer remaining on the peripheral surface ofthe photosensitive drum 1 after the image transfer. The charge roller 2,development unit 4, and cleaner unit 50 are placed in the adjacencies ofthe peripheral surface of the photosensitive drum 1. The main assemblyof the image forming apparatus is provided with a plurality of 1oscanner units 3(3Y, 3M, 3C, and 3K) for forming an electrostatic latentimage on the peripheral surface of the photosensitive drum 1.

The image formation process of this image forming apparatus is asfollows: First, the peripheral surface of the photosensitive drum 1 isuniformly charged by the charge roller 2 as a charging means. Then, theuniformly charged peripheral surface of the photosensitive drum 1 isexposed to a beam of laser light projected by the scanner unit 3 whilebeing modulated with video signals, forming thereby an electrostaticlatent image on the peripheral surface of the photosensitive drum 1.This electrostatic latent image is developed by the developing means(development roller 40) of the development unit 4, which uses developer.

The conveying means for conveying a recording medium to the cartridge 7has the following structure. In a cassette 17 located in the bottomportion of the apparatus main assembly 100A, a plurality of recordingmediums S are stored. The recording mediums S are fed out of thecassette 17 by a feed roller 18 while being separated one by one, andare sent to a pair of registration rollers 19. Then, each recordingmedium S is conveyed by the pair of registration roller 19 to theelectrostatic transfer belt 11 in synchronism with the progression of animage forming operation. Then, the recording medium S is conveyed by theelectrostatic transfer belt 11 sequentially along the four cartridges 7.The transfer belt 11 is stretched around, and suspended by, the rollers13, 14 a, 14 b, and 15, and is circularly driven. The transfer belt 11keeps the recording medium S electrostatically adhered thereto, andconveys the recording medium S through the location, in which therecording medium S is placed in contact with the peripheral surface ofthe photosensitive drum 1.

In this embodiment, the conveying means is made up of the feed roller18, pair of registration rollers 19, electrostatic transfer belt 11, andpair of discharge rollers 23. The discharge roller 23 will be describedlater.

Within the loop formed by the transfer belt 11, four transfer rollers 12(12Y, 12M, 12C, and 12K) are placed in parallel in the positions inwhich they oppose the four photosensitive drums 1 (1Y, 1M, 1C, and 1K),respectively, and contact the transfer belt 11. In these positions, thedeveloper images, which are formed on the peripheral surfaces of thephotosensitive drums 1, one for one, and are different in color, aresequentially transferred in layers by the application of transfer biasto the transfer rollers 12, onto the recording medium S, while therecording medium S is conveyed by the transfer belt 11. As a result, acolor developer image is formed on the recording medium S.

After the formation of the color developer image on the recording mediumS, the recording medium S is conveyed to a fixing station 20 in whichthe next step is carried out. In the fixing station 20, the colordeveloper image is fixed to the recording medium S by the application ofheat and pressure. Thereafter, the recording medium S is discharged bythe pair of discharge rollers 23 into a delivery station 24 located ontop of the apparatus main assembly.

[Structure of Process Cartridge]

Next, referring to FIGS. 3 and 4, the general structure of the cartridge7 will be described. In this embodiment, the cartridge 7Y having yellowdeveloper, cartridge 7M having magenta developer, cartridge 7C havingcyan developer, and cartridge 7K having black developer are identical instructure. Each cartridge 7 has the photosensitive drum 1, and one ormore processing means, which are a charging means (processing means),developing means (processing means), and cleaning means (processingmeans). The processing means are placed in the adjacencies of theperipheral surface of the photosensitive drum 1.

The photosensitive drum 1 comprises a cylindrical substrate 63, forexample, an aluminum cylinder, and a photosensitive layer coated on theperipheral surface of the aluminum cylinder 63. The photosensitive drum1 is rotatably supported by the pair of shafts attached to thelengthwise ends of the aluminum cylinder 63. To one of the lengthwiseends of the photosensitive drum 1, the driving force from a motor istransmitted, rotating the photosensitive drum 1 (in counterclockwisedirection).

The charging means is for uniformly charging the peripheral surface ofthe photosensitive drum 1. In this embodiment, a charge roller 2, whichis electrically conductive, is employed as the charging means. Thecharge roller 2 is kept in contact with the peripheral surface of thephotosensitive drum 1 by a pressure generating means such as a pair ofsprings. As charge bias is applied to the charge roller 2, theperipheral surface of the photosensitive drum 1 is uniformly charged bythe charge roller 2.

The developing means, which uses developer, is for developing anelectrostatic latent image formed on the peripheral surface of thephotosensitive drum 1. To describe the structure of the developingmeans, it comprises a developer container (developer storage portion) 41in which developer is contained, and from which the developer is sent toa developer supply roller 43 by a developer sending mechanism 42 locatedwithin the developer container 41. The developer supply roller 43 isrotated in the clockwise direction (FIG. 2). It supplies the developmentroller 40 with the developer, and also, strips the developer from thedevelopment roller 40 after the development. The developer supplied tothe development roller 40 is evenly coated, while being given electriccharge, on the peripheral surface of the development roller 40 by adevelopment blade 44 kept pressured against the peripheral surface ofthe development roller 40. As development bias is applied to thedevelopment roller 40 from the apparatus main assembly 100A, thedevelopment roller 40 develops the latent image; it adheres thedeveloper to the latent image. The development roller 40 is positionedin parallel to the photosensitive drum 1, and is rotated in theclockwise direction indicated by an arrow mark in FIG. 2.

The developer container 41, developer supply roller 43, developmentroller 40, and development blade 44 belong to the development unit 4.

The cleaning means is for removing the developer remaining on theperipheral surface of the photosensitive drum 1 after the developerimage is transferred from the photosensitive drum 1. The cleaning blade60 as the cleaning means belongs to the cleaner unit 50. In other words,the cleaner unit 50 comprises the cleaning blade 60 for removing thedeveloper remaining on the peripheral surface of the photosensitive drum1, a removed developer storage chamber (removed developer storingportion) 55 for storing the developer removed from the peripheralsurface of the photosensitive drum 1 by the cleaning blade 60, and aflexible sheet 80 for preventing the developer removed by the blade 60from leaking from the cleaner unit frame 51. The sheet 80 is positionedso that a small amount of contact pressure is generated between its tipand peripheral surface of the photosensitive drum 1.

The unit 50 also comprises photosensitive drum 1 and charge roller 2, inaddition to the cleaning means, and is connected to the development unit4 so that the two units 50 and 4 are rotatable relative to each other.In other words, the cartridge 7 is made up of the cleaner unit 50 anddevelopment unit 4.

To describe in detail, the photosensitive drum 1 is rotatably attachedto the frame 51 of the cleaner unit 50, with a pair of bearings 30 and31 placed between the photosensitive drum 1 and frame 51. Further, thecharge roller 2, cleaning blade 60, and sheet 80 are placed in contactwith the photosensitive drum 1, as described before. Further, theremoved developer storage chamber 55 is a part of the cleaner unit 50.

The development unit 4 has a frame 46 formed by joining two separateframes 45 a and 46 b by ultrasonic welding. To this development unitframe 46, the development roller 40, developer container 41, developersupply roller 43, and development blade 44 are attached.

The development unit 4 is connected to the cleaner unit 50 in thefollowing manner. First, the two units 4 and 50 are positioned so thatthe connective holes 47 and 48 of the development unit 4, located at thelengthwise ends of the development unit frame 46, align with thesupportive holes 52 and 53 of the cleaner unit 50, located at thelengthwise ends of the cleaning unit frame 51, respectively. Then, apair of pins (unshown) are inserted through the holes 47 and 52, andholes 48 and 53, from outside the lengthwise ends of cleaner unit frame51. As a result, the development unit 4 is connected to the cleaner unit50 so that it is rotatable relative to the cleaner unit 50.

The development unit 4 is kept under the pressure generated by a pair ofsprings (unshown), or the like elastic members, toward the cleaner unit50, in order to keep a pair of spacer rings (unshown) fitted around thedevelopment roller 40, pressed upon the peripheral surface of thephotosensitive drum 1. The pair of springs (unshown) are attached to thelengthwise ends of the unit 50, one for one.

[Structure for Mounting Process Cartridge into Main Assembly of ImageForming Apparatus or Removing it Therefrom]

Next, referring to FIGS. 3 and 4, the structure of the means forremovably mounting the cartridge 7 into the main assembly 100A of theimage forming apparatus 100 will be described.

Referring to FIG. 4, the image forming apparatus main assembly 100A isprovided with a front cover 100, which is hinged to the main assembly100A. The aforementioned transfer belt 11 is attached to the inward sideof the front cover 101. In other words, the front cover 101 and transferbelt 11 are attached to the apparatus main assembly 100A so that theycan be opened or closed against the apparatus main assembly 100A. Whenthe front cover 100 and transfer belt 11 are open, the cartridge 7 canbe removably mounted into the main assembly 100A.

Referring to FIG. 3, the cartridge 7 is provided with a pair of guidingportions 30 a and 31 a, which are located at the lengthwise ends of thecartridge 7 to guide the cartridge 7 when mounting the cartridge 7 intothe apparatus main assembly 100A or removing it therefrom. The cartridge7 is also provided with a pair of handles 30 b and 31 b, which arelocated at the lengthwise ends of the cartridge 7.

As for the apparatus main assembly 100A, it is provided with a pair ofguide rails (unshown) for guiding the guiding portions 30 a and 31 a ofthe cartridge 7.

When mounting the cartridge 7 into the apparatus main assembly 100A, thecartridge 7 is to be inserted into the apparatus main assembly 100A sothat the guiding portions 30 a and 31 a follow the guide rails of theapparatus main assembly 100A. This makes it possible to properly mountthe cartridge 7 into the apparatus main assembly 100A. When taking thecartridge 7 out of the apparatus main assembly 100A, the cartridge 7 isto be pulled outward so that the guiding portions 30 a and 31 a followthe guide rails of the apparatus main assembly 100A. This makes iteasier to remove the cartridge 7 from the apparatus main assembly 100A.In other words, the provision of the guiding portions 30 a and 31 a andthe guiding rails makes it easier to mount or dismount the cartridge 7.

[Structure for Precisely Positioning Photosensitive Drum relative toMain Assembly of Image Forming Apparatus]

Next, referring to FIGS. 5-8, the structure for precisely positioningthe photosensitive drum 1 relative to the main assembly 100A of theimage forming apparatus will be described.

The main assembly 100A of the image forming apparatus is provided with adriving force transmitting mechanism for transmitting driving force tothe photosensitive drum 1.

Referring to FIGS. 5, 6, and 9, this diving force transmission mechanismof the apparatus main assembly 100A comprises a motor (unshown), and adriving gear 71 with which the apparatus main assembly 100A is providedto transmit the driving force from the aforementioned motor. The drivinggear 71 has a shaft portion 71 d, which projects from the center of thedriving gear 71. This shaft portion 71 d has a noncircular spiral hole71 a, the cross section (perpendicular to its axial direction) of whichhas a plurality of apexes. The transmission mechanism also comprises adrive shaft 70, which is put through the center portion of the drivinggear 71, and which is projecting from the center of the bottom wall ofthe spiral hole 71 a of the shaft portion 71 d; in other words, thedrive shaft 70 is put through the shaft portion 71 d. The end of thedrive shaft 70, on the shaft portion side, is made hemispheric, forminga hemispherical portion 70 a. The hemispherical portion 70 a ispositioned so that its center coincides with the axial line of thespiral hole 71 a, and slightly protrudes outward beyond the edge (endsurface) of the spiral hole 71 a.

Next, the driving force receiving mechanism with which the cartridge 7is provided will be described.

Referring to FIG. 6, the photosensitive drum 1 is provided with a pairof flanges 61 and 62, which are attached, one for one, to the lengthwiseends of the cylinder 63, the peripheral surface of which is coated withthe photosensitive layer. The flange 61 is provided with a shaft portion61 a, which is located at the outward end of the flange 61, and by whichthe photosensitive drum 1 is rotatably supported by a bearing 31 (FIG.3), whereas the flange 62 is provided with a shaft portion 62 a, whichis located at the outward end of the flange 62, and by which thephotosensitive drum 1 is rotatably supported by a bearing 30. Next,referring to FIG. 5, the shaft portion 61 a is provided with anoncircular spiral projection 61 b, as a portion for receiving thedriving force from the main assembly 100A of the image formingapparatus, the cross section of which has a plurality of apexes. As thecartridge 7 is mounted into the apparatus main assembly 100A, thisprojection 61 b fits into the aforementioned spiral hole 71 a, andreceives from the apparatus main assembly 100A the driving force forrotating the photosensitive drum 1. To describe in more detail, thedriving gear 71 is rotated, with the projection 61 b positioned in thespiral hole 71 a. Therefore, the rotational force from the driving gear71 is transmitted to the photosensitive drum 1 through the projection 61b, while the projection 61 b remains subjected to the force generated inthe direction to draw the projection 61 b into the hole 71 a, at theinterface between the projection 61 b and the wall of the spiral hole 71a.

Referring to FIG. 7, the projection 61 b is a blind center hole 65,which opens at the end surface of the projection 61 b, on the mainassembly side. This hole 65 has: the bottom 65 a (bottom surface) whichcomes into contact with the tip (peak) 70 a 2 of the hemisphericalportion 70 a of the of the drive shaft 70, which is protruding beyondthe edge of the spiral hole 71 a; and the lateral surface 65 b, whichcomes into contact with the base portion 70 a 1 of the hemisphericalportion 70 a of the drive shaft 70. In other words, as the projection 61b having entered the spiral hole 71 a receives from the apparatus mainassembly 100A the driving force for rotating the photosensitive drum 1,the bottom 65 a of the hole 65 of the projection 61 b comes into contactwith the tip (peak) 70 a 2 of the hemispherical portion 70 a of thedrive shaft 70, and the lateral surface 65 b of the hole 65 of theprojection 61 b comes into contact with the base portion 70 a 1 of thehemispherical portion 70 a of the drive shaft 70. In this embodiment,the lateral wall 65 b is made roughly perpendicular to the bottom 65 a.To describe in more detail, first, the projection 61 b enters the hole71 a, and then, the tip (peak) 70 a 2 of the hemispherical portion 70 acomes into contact with the bottom 65 a (contact point 65 a 1 in FIG.7). The tip (peak) 70 a 2 comes into contact with the bottom 65 a insuch a manner that after the contact between the tip (peak) 70 a 2 andbottom 60 a, it virtually coincides with the axial line of thephotosensitive drum 1. Further, the base portion 70 a 1 of thehemispherical portion 70 a comes into contact with the lateral surface65 b (contact point 61 a 2 in FIG. 7) in such a manner that therotational axis of the base portion 7 a 2 virtually coincides with theaxial line of the photosensitive drum 1. Thus, as the driving gear 71 isrotated, the rotational force from the driving gear 71 is transmitted tothe photosensitive drum 1 through the interface between the wall of thespiral hole 71 a and the projection 61 b, while the projection 61 bremains subjected to the force (thrust) generated in the direction todraw the projection 61 b into the spiral hole 71 a at the interface. Asa result, the hemispherical portion 70 a is drawn deeper into the hole65, and the tip (peak) 70 a 2 of the hemispherical portion 70 a isplaced in contact with the bottom 65 a by the above described projectiondrawing force (thrust), ensuring that the tip (peak) 70 a 2 comes intocontact with the bottom 65 a, and the base portion 70 a 1 comes intocontact with the lateral surface 65 b. The cross section of the hole 65perpendicular to the axial line of the flange 61 is circular. In otherwords, the hole 65 is cylindrical. The internal diameter of the hole 65and the external diameter of the hemispherical portion 70 a are maderoughly the same, allowing therefore the hemispherical portion 70 a toenter the hole 65. The reason why the two diameters are roughly thesame, that is, the external diameter of the hemispherical portion 70 ais made slightly smaller than the internal diameter of the hole 65, isto take the manufacture tolerance into consideration, in order to ensurethat the hemispherical portion 70 a is allowed to enter the hole 65. Thehole 65 is positioned so that its axial line coincides with the axialline of the photosensitive drum 1, and the base portion 70 a 1 of thehemispherical portion 70 a contacts the lateral surface 65 b of the hole65 so that the axial line of the base portion 70 a 1 coincides with thatof the photosensitive drum 1. Further, the tip (peak) 70 a 2 of thehemispherical portion 70 a contacts the flat bottom 65 a of the hole 65.

The tip (peak) 70 a 2 of the hemispherical portion 70 a is placed incontact with the bottom 65 a of the hole 65 in the lengthwise directionof the photosensitive drum 1, that is, the direction axial direction(thrust direction). As a result, the position of the photosensitive drum1 relative to the apparatus main assembly 100A in terms of thelengthwise (thrust) direction of the photosensitive drum 1 is fixed.Further, the base portion 70 a 1 of the hemispherical portion 70 acontacts the lateral surface 65 b, whereby the position of thephotosensitive drum 1 relative to the apparatus main assembly 100A interms of the direction perpendicular to the lengthwise direction of thephotosensitive drum 1 is fixed; in other words, the photosensitive drum1 is precisely positioned relative to the apparatus main assembly 100Ain terms of the radius direction (of the photosensitive drum 1).Further, in terms of the lengthwise direction of the photosensitive drum1, the hole 65 is positioned so that it overlaps with the hemisphericalportion 70 a, making it possible to reduce the dimension of theapparatus main assembly 100A in terms of the lengthwise direction of thephotosensitive drum 1.

Referring to FIG. 7, in this embodiment, the hole 71 a is spiral, andits cross section is roughly triangular; it is preferred that the crosssection of the 71 a is roughly in the form of an equilateral triangle.The projection 61 b is also spiral, and its cross section is alsoroughly triangular; it is preferred that the cross section of theprojection 61 b is roughly in the form of an equilateral triangle. Itshould be noted that when the cross sections of the hole 71 a andprojection 61 b are is roughly in the form lo of an equilateraltriangle, the level of accuracy at which the axial lines of the hole 71a and projection 61 b align with each other is much better thanotherwise; in other words, the level of accuracy at which the axiallines of the driving gears 71 and photosensitive drum 1 align with eachother is much better than otherwise.

In this embodiment, the hole 71 a is in the form of a spiral hole, thecross section of which is roughly triangular, and the projection 61 b isin the form of a spiral pillar, the cross section of which is alsotriangular. However, this embodiment is not intended to limit the scopeof the present invention. That is, the configuration of the hole 71 amay be different from the one in this embodiment, as long as the hole 71a is in the form of a spiral hole, the cross section of which isnoncircular and has a plurality of apexes. Similarly, the configurationof the projection 61 b may be different from the one in this embodiment,as long as the projection 61 b is in the form of a spiral projection,the cross section of which is noncircular and has a plurality of apexes.In other words, as long as the projection 61 b, which fits into thenoncircular spiral hole, the cross section of which has a plurality ofapexes, is such a noncircular spiral projection, the cross section ofwhich has a plurality of apexes, the configuration of the projection 61b may be different from the one in this embodiment. With the hole 71 aand projection 61 b structured as described above, as the driving gear71 is rotated while the projection 61 b is in the hole 71 a, the axiallines of the projection 61 b and hole 71 a align with each other inpractical terms. In other words, as long as the projection 61 b and hole71 a are structured so that the projection 61 b receives the drivingforce from the apparatus main assembly 100A while remaining subjected tothe force generated in the direction to draw the projection 61 b intothe hole 71 a by the interface between the projection 61 b and thelateral surface of the hole 71 a, the configurations of the projection61 b and hole 71 a do not need to be limited to those described above.

Referring to FIGS. 6 and 8, the external diameter X of the shaft portion71 d of the driving gear 71 is set to be smaller than the internaldiameter Y of the hole 74 a of the supporting frame (supporting member)74 (X<Y) (FIGS. 6 and 8). Therefore, the shaft portion 71 d is allowedto move in the radius direction of the shaft 71 d, within the hole 74 a.While the photosensitive drum 1 is in connection with the driving gear71, that is, while the projection 61 b is in the hole 71 a, the drivinggear 71 does not come into contact with the supporting member 74 of theapparatus main assembly 100A; in other words, the shaft portion 71 ddoes not come into contact with the internal surface of the hole 74 a.Therefore, the driving gear 71 smoothly rotates. Incidentally, while theprojection 61 b is not in contact with the internal surface of the hole71 a, the shaft portion 71 d is in contact with the internal surface ofthe hole 74 a; in other words, the shaft portion 71 d is supported bythe supporting frame (member) 74. The gear positioning portion 71 c ofthe driving gear 71, that is, the portion which is positioned oppositeto the photosensitive drum 1, is supported by the supporting frame 72 ofthe apparatus main assembly 100A, with a bearing 73 placed between thepositioning portion 71 c and supporting frame 72; in other words, it issupported by the supporting frame 72, with the provision of a minimumamount of gap, between the positioning portion 71 c and supporting frame72 (bearing 73), necessary to allow the driving gear 71 to sliderelative to the apparatus main assembly 100A. Therefore, while theaforementioned rotational driving force is transmitted, the position ofthe driving gear 71 relative to the photosensitive drum 1 remains fixedin terms of the radius direction of the photosensitive drum 1. In otherwords, the position of the driving gear 71 in terms of its radiusdirection is fixed as the position of the photosensitive drum 1 in termsof its radius direction becomes fixed. Further, as described above, thelengthwise ends of the photo-sensitive drum 1 are supported by the pairof bearings 30 and 31 with which the cartridge frame is provided.Therefore, the position of the photosensitive drum 1 in terms of itsradius direction becomes fixed as its lengthwise ends are supported bythe pair of bearings 30 and 31. Therefore, the axial line of the driveshaft 70 of the apparatus main assembly 100A, and the axial line of thephotosensitive drum 1 coincide with each other. Incidentally, the driveshaft 70 is integrally attached to the driving gear 71, and the driveshaft 70 and driving gear 71 are attached to the bearing 73 so that theydo not move relative to the apparatus main assembly 100A in their axialdirections. In comparison, the photosensitive drum 1 is supported by thebearings 30 and 31 so that it is allowed to move relative to theapparatus main assembly 100A in its axial direction.

Even if the photosensitive drum 1 and driving gear 71 are positionedrelative to each other so that their axial lines coincide with eachother, the axial line of the drive shaft 70 sometimes becomes slightlytilted relative to the axial line of the photosensitive drum 1, becauseof the tolerances of the components for supporting them. Hereafter, theangle of this tilt will be referred to as declination angle θ. Referringto FIG. 7, in this embodiment, the photosensitive drum 1 is preciselypositioned by placing the tip (peak) 70 a 2 of the hemispherical portion70 a in contact with the bottom 65 a of the hole 65, in terms of thelengthwise direction of the photosensitive drum 1. Therefore, as the tip(peak) 70 a 2 comes into contact with the bottom 65 a, a gap U is alwaysleft between the end surface 61 b 1 of the projection 61 b and thebottom 70 a 1 of the hole 71 a. In this embodiment, it is ensured thateven if the axial line of the drive shaft 70 slightly (at declinationangle of θ) deviates from that of the photosensitive drum 1, the gap Ualways remains between the end surface 61 b 1 of the projection 61 b andthe bottom 70 a 1 of the hole 71 a. Therefore, the tip (peak) 70 a 2 ofthe hemispherical portion 70 a never fails to contact the bottom 65 a ofthe hole 65. Therefore, even if the axial line of the driving gear 71(drive shaft 70) tilts relative to the axial line of the photosensitivedrum 1, the rotational velocity of the photosensitive drum 1 is notaffected. In other words, in this embodiment, even if the axial line ofthe drive shaft 70 deviates by the declination angle θ, the rotationalvelocity of the photosensitive drum 1 does not become irregular. This isbecause the tip (peak) 70 a 2 of the hemispherical portion 70 a and thebottom 65 a of the hole 65 contact each other in such a manner that thecontact point between them remains coincident with the axial line of thephotosensitive drum 1. In other words, even if the axial line of thedrive shaft 70 becomes tilted by the declination angle θ, the tip (peak)70 a 2 contacts the bottom 65 a so that the contact point between themcoincides with the axial line of the photosensitive drum 1. Therefore,the photosensitive drum 1 of the cartridge 7 is prevented from becomingirregular in rotational velocity. Therefore, it is possible to preventthe occurrence of color deviation attributable to the irregularity inthe rotational velocity of the photosensitive drum 1, when forming afull-color image.

Incidentally, designated by a referential number 71 b is the actual gearportion of the driving gear 71. More specifically, the actual gearportion 71 b is helical.

As described above, in this embodiment, the position of thephotosensitive drum 1 relative to the apparatus main assembly 100A interms of the axial direction of the photosensitive drum 1 is fixed bythe force generated in the direction to draw the projection 61 b intothe hole 71 a as the driving gear 71 is rotated after the projection 61b fits into the hole 71 a. Further, the tip (peak) 70 a 2 of thehemispherical portion 70 a is placed in contact with the bottom 65 a ofthe hole 65. Therefore, even if the axial line of the driving gear 71becomes tilted relative to the axial line of the photosensitive drum 1,the rotational velocity of the photosensitive drum 1 does not becomeirregular. Therefore, the photo- sensitive drum 1 of one cartridge 7does not become different in rotation from the photosensitive drums 1 inthe other cartridges 7 In other words, this embodiment makes it possibleto precisely control the rotation of the photosensitive drum 1, makingit possible to minimize the color deviation attributable to theirregularity in the rotation of the photo-sensitive drum 1. Therefore,this embodiment can yield a color image of higher quality.

At this time, referring to FIG. 10, the results of the comparisonbetween the above described embodiment of the present invention, and thecomparative example, will be described. FIG. 10 provides the data forcomparing the above described embodiment of the present invention, andthe comparative example, in terms of the irregularity in the rotation ofthe photosensitive drum. In the case of the comparative example, thestructure for positioning the photosensitive drum relative to theapparatus main assembly in terms of the lengthwise direction of thephotosensitive drum is such that the photosensitive drum is positionedrelative to the apparatus main assembly by placing the flat bottomsurface of the hole provided on the apparatus main assembly side, incontact with the flat end surface of the projection provided on thecartridge side. The comparative example was tested, with the declinationangle set to 0.3°. To compare the above described embodiment of thepresent invention with the comparative example, the embodiment of thepresent invention was tested, with the declination angle set also to0.30. FIG. 10(a) shows the irregularity in the rotation of thephotosensitive drum 1 in the above described embodiment, and FIG. 10(b)shows the irregularity in the rotation of the photosensitive drum in thecomparative example. In both figures, the axis of ordinates representsthe amount of the fluctuation in the rotational velocity of thephotosensitive drum, and axis of abscissas represents the elapsed time.As will be evident from these graphs, the photosensitive drum 1 in theembodiment of the present invention, the test results of which are givenin FIG. 10(a), is smaller in the amount of the fluctuation in therotational velocity per unit of time (per rotation) than thephotosensitive drum in the comparative example, the test results ofwhich are given in FIG. 10(b).

In other words, in the case of the embodiment of the present invention,even when the axial line of the driving gear 71 became tilted relativeto the axial line of the photosensitive drum 1, the rotation of thephotosensitive drum 1 did not become irregular. This is because theaforementioned tip (peak) contacted the aforementioned bottom in such amanner that the contact point between them was always coincident withthe axial line of the photosensitive drum. In other words, even when theaxial line of the driving gear 71 became tilted relative to the axialline of the photosensitive drum 1, the tip (peak) of the hemisphericalportion contacted the aforementioned bottom at the axial line of thephotosensitive drum 1.

Incidentally, when measuring the amount of the irregularity in therotational velocity of the photosensitive drum, the amount of the torqueapplied to rotate the photosensitive drum 1 was set to 3 kgf cm, inorder to match the amount of the torque applied for the test to theamount of the torque applied to rotate the photosensitive drum in anactual cartridge.

Next, referring to FIG. 8, the structural arrangement for grounding thephotosensitive drum 1 to the apparatus main assembly 100A through thehemispherical portion 70 a will be described. The other structuralarrangements are the same as those described above, and therefore, theirdescription given above is to be referred to for the descriptions of thestructural arrangements other than that for the grounding structure.

The drive shaft 70 and hemispherical portion 70 a is made electricallyconductive, and one end of a contacting member 77 is placed in contactwith the rear end of the driving shaft 70, as shown in FIG. 8, and theother end of the contacting member 77 is attached to the supportingframe 72. The contacting member 77 and supporting frame 72 are formed ofmetallic plate and are electrically conductive. Therefore, thehemispherical portion 70 a, drive shaft 70, contacting member 77, andsupporting frame 72 are electrically connected. Further, in thisembodiment, the bottom 65 a of the hole 65 (FIG. 8) is covered with oneend of a piece of electrically conductive metallic plate (photosensitivedrum grounding contact) 76, the other end of the which is electricallyconnected to the electrically conductive cylinder 63 of thephotosensitive drum 1. In other words, within the hole 65, one end ofthe metallic plate 76, as a grounding contact, electrically connected tothe cylinder 63, is position in a manner to cover the bottom 65 a of thehole 65, so that as the projection 61 b fits into the hole 71 a andreceives from the apparatus main assembly 100A the force forrotationally driving the photosensitive drum 1, the hemisphericalportion 70 a is pressed on the metallic grounding plate 76 by theaforementioned force generated in the direction to draw the projection61 b into the hole 71 a. In other words, this metallic grounding plate76 comes into contact with the tip (peak) 70 a 2 of the hemisphericalportion 70 a, when the cartridge 7 is in the apparatus main assembly100A. Further, the one end of the metallic grounding plate 76, whichcovers the bottom 65 a of the hole 65, and with which the tip (peak) 70a 2 comes into contact, is flat. Therefore, while the rotational forceis transmitted to the photosensitive drum 1, with the projection 61 bbeing in the hole 71 a, the photo-sensitive drum 1 remains electricallyconnected to the apparatus main assembly 100A through the groundingmetallic plate 76, hemispherical portion 70 a, drive shaft 70,contacting member 77, and supporting frame 72, because while therotational force is transmitted to the photosensitive drum 1 from theapparatus main assembly 100A, the aforementioned force generated in thedirection to draw the projection 61 b into the hole 71 a keeps thehemispherical portion 70 a pressed upon the metallic grounding plate 76,ensuring that the hemispherical portion 70 a and metallic groundingplate 76 remain electrically connected. In addition, the resiliency ofthe hemispherical portion 70 a keeps the metallic grounding plate 76resiliently connected to the hemispherical portion 70 a, also ensuringthat the two remain electrically connected. Therefor, the photosensitivedrum 1 is reliably grounded and remain grounded.

With the provision of the above described structural arrangement, thepoint of the hemispherical portion 70 a, by which the hemisphericalportion 70 a contacts the metallic grounding plate 76 (and vice versa),that is, by which the hemispherical portion 70 a keeps thephotosensitive drum 1 electrically connected to the drive shaft 70, doesnot slide on the metallic grounding plate 76; in other words, it remainsin contact with only a single spot of the metallic grounding plate 76.This is because the photosensitive drum 1 and drive shaft 70 rotatetogether. Therefore, it is ensured that the cartridge 7 removablymountable in the apparatus main assembly 100A is electrically connected,and remains connected, to the apparatus main assembly 100A.

Further, the force generated in the direction to draw the projection 61b into the hole 71 a during the transmission of the rotational drivingforce is utilized as the pressured to keep the hemispherical portion 70a pressed on the metallic grounding plate 76. Therefore, a user does notneed to be concerned about the fatigue of the components through whichthe photosensitive drum 1 is grounded. Further, the contact pressure isgenerated only during the transmission of the rotational driving force,and the force which works in the direction to draw the projection 61 binto the hole 71 a is not generated (projection drawing force is turnedoff) while the driving force is not transmitted; it is generated(projection drawing force is turned on) only during the transmission ofthe driving force. Thus, as the projection drawing force is turned on oroff, the slight misalignment occurs between the axial lines of thephotosensitive drum 1 and drive shaft 70, and this misalignment has theeffect of causing the hemispherical portion 70 a and metallic groundingplate 76 to wipe each other.

Further, referring to FIG. 5, the hole 65 is shaped so that its crosssection perpendicular to the axial line of the hole 65 becomes circular,minimizing the amount of the space necessary for the hole 65. Therefore,it is possible to reduce the size of the projection 61 b withoutreducing the projection 61 b in strength. Accordingly, it is possible toreduce in size the hole 71 a into which the projection 61 b fit, makingit therefore possible to reduce in size the main assembly 100A of theimage forming apparatus.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth, and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Applications Nos.140695/2004 and 283318/2004 filed May 11, 2004 and Sep. 29, 2004,respectively which is hereby incorporated by reference.

1. An electrophotographic photosensitive drum for a process cartridgedetachably mountable to a main assembly of an electrophotographic imageforming apparatus for forming an image on a recording material, the mainassembly including a motor, a main assembly gear for transmitting adriving force from the motor, and a non-circular twisted hole having asection with a plurality of corner portions provided at a centralportion of the main assembly gear, the non-circular twisted hole beingrotatable integrally with the main assembly gear, saidelectrophotographic photosensitive drum comprising: (a) a cylinderhaving a photosensitive layer on a peripheral surface thereof; and (b) anon-circular twisted projection provided on one longitudinal end of saidcylinder and having a section with a plurality of corner portions, saidnon-circular twisted projection being engageable with the hole of themain assembly of the apparatus to receive a rotational driving force forrotating said electrophotographic photosensitive drum from the mainassembly of the apparatus when said process cartridge is mounted to themain assembly of the apparatus, wherein a recess is formed in a centralportion of said projection and has a bottom portion and a side surfaceportion, wherein when said projection receives a pulling force towardthe hole by rotation of the main assembly gear with said projection andthe hole being engaged with each other, said bottom portion contacts aspherical surface portion provided at a central portion of the hole, andsaid side surface portion contacts the spherical surface portion, andwherein when said electrophotographic photosensitive drum is mounted tothe main assembly of the apparatus, and said electrophotographicphotosensitive drum receives the rotational driving force for rotatingsaid electrophotographic photosensitive drum from the main assembly ofthe apparatus, an end of the spherical surface portion contacts saidbottom portion, and the spherical surface portion contacts said sidesurface portion.
 2. An electrophotographic photosensitive drum accordingto claim 1 or 2, wherein the spherical surface portion iselectroconductive and is electrically connected with the main assemblyof the apparatus, wherein said electrophotographic photosensitive drumfurther comprises a grounding contact in said recess, wherein saidgrounding contact is electrically connected with said cylinder and ispositioned at said bottom portion, and wherein said grounding contact isurged to the spherical surface portion by a pulling force when saidelectrophotographic photosensitive drum receives the rotational drivingforce from the main assembly of the apparatus through engagement of saidprojection with the hole.
 3. An electrophotographic photosensitive drumaccording to claim 1 or 2, wherein said recess has a circular section.4. An electrophotographic photosensitive drum according to claim 3,wherein the end of the spherical surface portion contacts a flat surfaceportion of said bottom portion.
 5. A process cartridge detachablymountable to a main assembly of an electrophotographic image formingapparatus for forming an image on a recording material, the mainassembly including a motor, a main assembly gear for transmitting adriving force from the motor, and a non-circular twisted hole having asection with a plurality of corner portions provided at a centralportion of the main assembly gear, the non-circular twisted hole beingrotatable integrally with the main assembly gear, said process cartridgecomprising: (a) electrophotographic photosensitive drum; (b) processmeans actable on said electrophotographic photosensitive drum; and (c) anon-circular twisted projection provided on one longitudinal end of saidelectrophotographic photosensitive drum and having a section with aplurality of corner portions, said non-circular twisted projection beingengageable with the hole of the main assembly of the apparatus toreceive a rotational driving force for rotating said electrophotographicphotosensitive drum from the main assembly of the apparatus when saidprocess cartridge is mounted to the main assembly of the apparatus,wherein a recess is formed in a central portion of said projection andhas a bottom portion and a side surface portion substantiallyperpendicular to said bottom portion, wherein when said projectionreceives a pulling force toward the hole by rotation of the mainassembly gear with said projection and the hole being engaged with eachother, said bottom portion contacts a spherical surface portion providedat a central portion of the hole, and said side surface portion contactsthe spherical surface portion, and wherein when said electrophotographicphotosensitive drum is mounted to the main assembly of the apparatus,and said electrophotographic photosensitive drum receives the rotationaldriving force for rotating said electrophotographic photosensitive drumfrom the main assembly of the apparatus, an end of the spherical surfaceportion contacts said bottom portion, and the spherical surface portioncontacts said side surface portion.
 6. A process cartridge according toclaim 5, wherein the spherical surface portion is electroconductive andis electrically connected with the main assembly of the apparatus,wherein said electrophotographic photosensitive drum further comprises agrounding contact in said recess, said grounding contact beingelectrically connected with a cylinder of said electrophotographicphotosensitive drum and being positioned at said bottom portion, saidgrounding contact being urged to the spherical surface portion by apulling force when said electrophotographic photosensitive drum receivesthe rotational driving force from the main assembly of the apparatusthrough engagement of said projection with the hole.
 7. A processcartridge according to claim 5 or 6, wherein said recess has a circularsection.
 8. A process cartridge according to claim 7, wherein the end ofthe spherical surface portion contacts a flat surface portion of saidbottom portion.
 9. An electrophotographic image forming apparatus forforming an image on a recording material, said electrophotographic imageforming apparatus comprising: (a) a motor; (b) a main assembly gearconfigured and positioned to transmit a driving force from said motor,wherein a non-circular twisted hole is provided in a central portion ofsaid main assembly gear and has a section with a plurality of cornerportions, the non-circular twisted hole being rotatable with said mainassembly gear, and wherein a spherical portion is provided in a centralportion of the hole; (c) a mounting portion in a main assembly of saidapparatus; and (d) a process cartridge detachably mounted to saidmounting portion, said process cartridge including; anelectrophotographic photosensitive drum; process means actable on saidelectrophotographic photosensitive drum; a non-circular twistedprojection provided on one longitudinal end of said electrophotographicphotosensitive drum and having a section with a plurality of cornerportions, said non-circular twisted projection being engage able withthe hole to receive a rotational driving force from said main assemblyof said apparatus when said process cartridge is mounted to saidmounting portion of said main assembly of said apparatus, and wherein arecess is formed in a central portion of said projection and has abottom portion and a side surface portion substantially perpendicular tosaid bottom portion, wherein when the hole receives a pulling forcetoward said projection by rotation of said main assembly gear with saidprojection and the hole being engaged with each other, said bottomportion contacts an end of said spherical surface portion, and said sidesurface portion contacts said spherical surface portion; and (e) feedingmeans for feeding the recording material, wherein when said processcartridge is mounted to said main assembly of said apparatus, and saidelectrophotographic photosensitive drum receives the rotational drivingforce for rotating said electrophotographic photosensitive drum fromsaid main assembly of said apparatus, the end of said spherical surfaceportion contacts said bottom portion, and said spherical surface portioncontacts said side surface portion.
 10. An apparatus according to claim9, wherein said spherical surface portion is electroconductive and iselectrically connected with the main assembly of [[the]] said apparatus,said process cartridge has a grounding contact in the recess, saidgrounding contact being electrically connected with a cylinder of saidelectrophotographic photosensitive drum and comprising said bottomportion, and being urged to said spherical surface portion by a pullingforce when said electrophotographic photosensitive drum receives thedriving force from the main assembly of said apparatus throughengagement of said projection with the hole.
 11. An apparatus accordingto claim 9 or 10, wherein said electrophotographic image formingapparatus is a full-color electrophotographic image forming apparatuscapable of receiving a plurality of said process cartridges.